Process for increasing the electrical conductivity and the flexibility of metals or alloys



Dec. 11, 1928. I v 1,695,044

K. HALLMANN PROCESS FOR INCREASING THE ELECTRICAL CONDUC'IIVITY AND THE FLEXIBILITY or METALS on ALLOYS Filed Sept. 21. 1922 a4 33-;32031, s 29 26 z? 2' Conductivity atzodegr ees centigrade 25 jected to a treatment which causes a reduc- Patented Dec. 11, 1 9 28.

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rnocassron racamsms, run nnscrnrcu. mumm -34m m ior mmune on. more? The present invention refers to a process. for improvin thev electrical qconductivit and the flexibilityofmetal's or alloys whic have, been cast in the fluid state and after 5 having-been solidified have been subjected ;to abut treatment- It is known that to increasethe hardness, the tenacity ofmetals' or alloys and the possibility of working themwith cut-ting tools, it is necessary to reheat I the metals oralloysafter casting or anneal ing and quenching'to relativelylow temperatures'which are below the known annealing temperatures. The metals or alloys, which have been thus treated, do however not show such a flexibility and electrical conductivity as is required for certain electrotechnical purposes, as for instance for electrical ,conducting wires-in free air. The said disadvantages are overcome by the present process.

The process consists in' t at .the heated metals as they comefrom the casting or an-- nealing process, are cooled down to ordinary,{ temperatures or near to them (for instanceabout degrees centigrade) and then subtion of their diameter, after which the metals or alloys'a're subjected to heat at tempera -tures below.those at which by the action of heat the strength and temper of the metals or alloys is diminished. The'eflect of the present process maybe illustrated by the following figures A wirepf pure aluminum for electrlcal free air conductors has an electrical conductivity of 33-34 at 20 degrees centi'grade and may bear 5-7 bendinglsover a radius equal to the diameter of e wire before a breakage will occur; I The wires of aluminum with 0.5-1% silicon, 02-10% iron and 0.1-0.7 ma esium afterhaving been hardened by eatin cooling and heating again torelatively ow temperatures, have an electrical conductivity of 28-29 and a flexibility of 0.5-1. If 'however,'the last mentioned wire is subjected to the present process, the electrical conductivity is increased'to 32-33, nearly equal to that of pure aluminum 'wire whereas the flexibility is 3-4., The strength ofthe wire subjected to the present process is not injured. I a

The reduction of the diameter of the metals or alloys in rods, bars or blocks'may be effected b a drawing or rolling process. For electrica conducting wires intended for use in free air a reduction of the diameter of about has been'found as suitable.

cooled to aboutJordinary temperatures, ,but

.for instance] from-2 to-3 days.''(The last ature of about 160 to 200 degrees centi e.

' lessen the effect secured bysubsequent treat:-

' 02-00% iron, 0.1-0.7 magnesium. The

" Themetals theann v I process or casting are preferably not reduce in diametergimmediately after having been i after having been allowed to some time,

named aging treatment may 'be. omitted, so that the cooled wires may be subjected immedlately to a, diminution of their diameter.) Afterthis the metals are heated to a temper- The decrease of the temperature from e an-- neahn process or 'cas'tmg, ma be efiected by chi mg for instance w1th o' or Water or by the action of air. The agents for lowering-the temperatureare selected according to the size of the objects. .For' example water is used for small objects and oil is used for] large objects. The cooling must be' efiected so. quick that the hot metal which has been sub ects to the casting or annealing tem erature, should not remain above a tempera re of 200- C. for a'periodsufiiciently' long to ment at 160-200 C. I w

The order of. the several stepsis important for. the success of'm rocess; First, the

metals or alloys must e- 'rought to the high annealing temperature of theannealingprocess or casting, then to a temperature at which no alteration 'of the 'internalfstructure will be efiected,then subjectedto thereduction of their diameter at. low tem erature (at ordinary temperature or. so cal ed inthe-cold) and finally subjected to a heating to'tempera tures between 160 and 200 degrees centigrade.

In'the following, some methods of carry out the present'process are explained for an alloy of aluminum with 0.5 to 1% silicon,

metals can as usual after the first annealing be drawn or -pressed,;which treatments cause alsoa diminution of their diameter and they are then subjected to the several steps of the present process.

2. The rolled bars are rolled at the usual rolling temperatures, say at about 350 to 450 degrees centigrade to round wire of about 10-20 millimeters diameter, cooled or allowed to cool and then annealed for about 2-3 hours at 540 to 560 degrees centigrade. After having been cooled quickly to about 160-200 degrees centigrade or about 20 degrees centigrade the wire of about 10-20 millimeters diameter is allowed to rest for about 2-3 days and. then rolled in the cold until the final diameter is obtained whereupon it is subjected for about 8-12 hours to 160 to 200 degrees centigrade and cooled.

3. The bars are annealed to about 550 to 580 degrees centigrade and pressed at temperatures of about 540 to 560 degrees centigrade to round wire of about 10 to 20 milllmeters diameter, the wire being forced either directly into water or 011 or it is pressed in the atmosphere and quickly cooled after the pressing operation by bringing it into water or oil, to temperatures of at least 160 to 200 degrees centigrade- After about 2 or 3 days the wireis drawn in the cold to the desired final diameter and subjected for about 8-12 hours to 160 to 200 degrees centigrade and cooled.

4. The bars are pressed as described in connection with Example 3 and slowly or quickly cooled. The pressed wire of about 10 to 20 millimeters diameters is annealed for about 2 to 3 hours at 540 to 560 degrees centigrade and uickly cooled in water or oil or another suit ible liquid to at least 160 to 200 degrees centigrade. After a lapse of about 2 to 3 days the wire is drawn or rolled in the cold to the desired final diameter and it is then subjected for about 8 to 12 hours to temperatures of about 160 to 200degrees centigrade and finally cooled.

The diameter ofthe preliminarily rolled or pressed wire is so chosen that it receives by the rolling or drawing in the cold a diminution of its diameter of about 90% at least when compared with the original preliminarily rolled or pressed wire. I

For an aluminum alloy composed of 9691.3% aluminum, 0.5to 1% silicon, 0.2 to 1% iron, 0.1 to 0.7% magnesium, 1-6%' copper the first annealing temperature which is suitable is about 500 to 520 degrees centirade. The further treatment is the same as escribed under Examples 1-4. If the prepressing, temperature of about 450 to 500 degrees centigrade is 'used.

In similar manner the process may be used for other metals or alloys suitable for being hardened, as for instance aluminum zinc, aluminum copper, aluminum silicon, aluminum cadmium, aluminum glucinum.

The annealing temperature used accordin to the present invention ispractically identical with the so-called condition diagram of the alloy to be treated, the abscissas being formed by the percentage of the alloying metal, the ordinate being formed by the temperature in degrees centigrade. The object of the treatment is to obtain an increase of thc hardness and at the same time of the electrical conductivity, whereas hitherto according to the known process especially of Van Oordt U. S. Patent 1,326,775 only an increase of the hardness and at the same time a diminution of the electrical conductivity could be obtained. The drawing shows a diagram illustrating the effect of the present process on a wire of 2-3 mm. diameter 1 corresponding to the strength of 30 kg. /mm. and 28 electrical conductivity obtained according to the process of Van Oordt U. S. A. Patent 1,326,7 75, 2 after the drawing at the cold or ordinary temperature and 3 after the hardening at temperatures between 160-200 degrees centigrade. The drawing shows that y the step of this invention the conductivity. is increased without diminishing the hardness thereof. That is, the aluminum or the like has been first recrystallized, then drawn, and it has then been subjected to a secondary heat treatment for lessening the internal'strains therein.

I claim:

1. The process for increasing the electrical conductivity and flexibility of aluminum alloys which consists in annealing aluminum alloys to recrystallization temperatures, reducing their cross-section by treatment in the cold and heating them to temperatures between 160 and 200 degrees centigrade.

2. The process for increasing the electrical conductivity of aluminum alloys by annealing said alloys to recrystallization temperatures, reducingthe cross sectionof such metals by treatment in the cold and heating to temperatures below 200 degrees centigrade.

In testimony whereof I hereunto aflix my signature.

DR. ING. KARL HALLMANN. 

